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Experimental Study on Strength Characteristics of Dispersion Clay

Author: TangZiQiang
Tutor: DangJinQian
School: Northwest University of Science and Technology
Course: Geotechnical Engineering
Keywords: dispersive clay loess strength characteristics moisture content dry density
CLC: TU41
Type: Master's thesis
Year: 2013
Downloads: 5
Quote: 0
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Abstract


Dispersive soil is special soil,it is dispersed in a low salinity of water (or pure water)because of the mutual repulsion forces over mutual attraction, carried away in case of theflowing water, brought serious harm to the actual project because of its low erosion resistanceand low impermeability, so dispersive soil has drawn much attention in recent years. So farthe research of dispersive soil focuses on its dispersion mechanism, identification methods,improved, and impermeability, the existing research results still lack enough theoreticalguidance for engineering practice, especially in the strength characteristics of dispersive soil,coupled with the rapid economic development, the number and size of engineeringconstruction is increasing rapidly in dispersion area, which makes the research on strengthcharacteristics of dispersive soil has more practical significance.In this paper, Yangling loess is compounded to dispersive soil and the conventionaltri-axial tests is used to study dispersive soil and loess’s strength characteristics at thedifferent initial moisture content and initial dry density, got the dispersive soil’s strengthcharacteristics under different initial conditions, analysis the dispersive soil’s stress-straincurve, specimen failure pattern and shear strength index changes with the initial conditions. Inaddition, compared with loess on stress-strain curve and shear strength index In the sameinitial conditions. The results show that:(1) Dispersive soil’s stress-strain curves shape is affected by the initial confiningpressure, moisture content and dry density obviously. dispersion clay’s stress-strain curvespresent the softening type when under the conditions of small confining pressure, lowmoisture content and high dry density,but it changes into the weak hardening type orhardening type when under the conditions of large confining pressure and high moisturecontent. The extermum principal stress difference increases with the confining pressure anddry density increased, with the increase of moisture content decreases.(2) Dispersive soil’s specimen failure pattern change with the initial conditions change,sample is brittle failure under low confining pressure and low moisture content, after shearmore appears shear zone, performance single shear failure or single local shear failure, stress-strain curves present the softening type. Under the same confining pressure andmoisture content, with the dry density increases, sample volume changes from shear to sheardilatancy, stress-strain curves changes from hardening to softening shape. In the same watercontent and dry density, confining pressure increasing makes the strain hardening and shearcontraction phenomenon more obvious. Under the same confining pressure and dry density,moisture content increasing makes the shear contraction phenomenon is more obvious, theshearing process with plastic failure, stress strain curve was hardening, no longer appear shearzone after shear, sample shows obviously drum shape.(3) Dispersion clay’s cohesion decreases with the increasing of moisture content. Inaddition, the impact of water will greatly increase with the thickening of its dry density, thetwo has a good correlation with exponential. Cohesion increases with the increase of drydensity, it has a bigger range in low moisture content. Internal friction angle decreases withthe moisture content increase, the two was the negative logarithm of the changing relationship.Internal friction angle has a small increase with the increasing of dry density.(4)The incorporation of sodium carbonate in this test doesn’t change the mechanicalproperties of loess, the preparation of dispersive soil and loess have the same stress-strainbehavior and shear strength characteristics.(5) Dispersive soil’s stress-strain curves and shear strength index under static anddynamic loads have the same variation with the change of initial conditions (confiningpressure, moisture content, dry density).

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